Energy accumulators are often used in systems, where a very high energy is necessary to be released for relatively short periods, and where the system has thereafter plenty of time to recharge the accumulator for the next release of high energy. Alternatively, they are also used for back-up purposes of hydraulic systems, where deficiencies like leakage may occur.
A typical example thereof is the landing gear braking systems of airplanes, where accumulators are known to be used for static braking of the landing gear, while on the ground, but also in some instances, for directly assisting braking itself.
In modern, often mobile, hydraulic systems the preferred item is a gas charged accumulator, but simple systems may be spring-loaded.
Other than for the security aspect of a back-up system an accumulator is typically used to be placed close to the pump with a non-return valve preventing flow back to it, in the best place to absorb pulsations of energy from the multi-piston pump. It also helps protect the system from fluid hammer. This protects system components; particularly pipe work, from both potentially destructive forces.
An additional benefit is the additional energy that can be stored while the pump is subject to low demand. The designer can use a smaller-capacity pump. The large excursions of system components, such as landing gear on a large aircraft, that require a considerable volume of fluid can also benefit from one or more accumulators. These are often placed close to the demand to help overcome restrictions and drag from long pipe work runs. The outflow of energy from a discharging accumulator is much greater, for a short time, than even large pumps could generate.
An accumulator can maintain the pressure in a system for periods when there are slight leaks without the pump being cycled on and off constantly. When temperature changes cause pressure excursions the accumulator helps absorb them. Its size helps absorb fluid that might otherwise be locked in a small fixed system with no room for expansion due to valve arrangement.
The gas pre-charge in an accumulator is set so that the separating bladder, diaphragm or piston does not reach or strike either end of the operating cylinder. The design pre-charge normally ensures that the moving parts do not foul the ends or block fluid passages. Poor maintenance of pre-charge can destroy an operating accumulator. A properly designed and maintained accumulator should operate trouble-free for years.
Although typically advantageous for aircrafts, the invention may be applied to a variety of energy consuming systems or more generally to any gas or liquid storage system, and will be exposed in the following description with reference to a hydraulic accumulator for the landing gear braking systems of airplanes, without being limited thereto.
International aviation security regulations an guidelines such as FAA or ESAS require, that the available energy stored in the accumulator such as for the braking fluid volume for braking the landing speed of an airplane down to taxiing speed, or for any other hydraulic system on board, must be constantly monitored and displayed to the pilot, in order to assure, that the pilot may take the necessary measures if the available energy for whatever system is not assured.
The braking of an airplane takes a considerable volume of braking fluid, and in order to provide this fluid in the required time to the brakes, one must either use an appropriately dimensioned fluid pump, which stays inactive for long periods of time, or use a smaller pump, which is just capable of accumulating the fluid under the required pressure in the accumulator during relatively long periods of non-use of the accumulator.